1. Field of the Invention
The present invention relates to a phase transformation memory and fabricating method thereof. More particularly, the present invention relates to a chalcogenide random access memory (CRAM) and method of fabricating the same.
2. Description of the Related Art
To satisfy the need for varieties, compactness, high density, low production cost and customization in memory products, an increasing large list of memory fabrication techniques are being investigated. One type of technique that receives particular attention is a phase-transformation memory. Phase-transformation is a process of changing a material from a non-crystalline state into a crystalline state or changing the crystalline state to a non-crystalline state. Because a non-crystalline material has a different light reflecting properties and electrical resistance from a crystalline material, the non-crystalline state and the crystalline state of the material can be used to represent a “0” and a “1” logic state in data storage. The aforementioned phase-transformation will occur when a laser beam or an electrical field is applied.
At present, a film fabricated using a compound from an alloy system material having erasable and phase-transformable properties called chalcogenide, consisting of germanium (Ge), antimony (Sb) and tellurium (Te) of the sulfur series, can be made to phase-transformation at a relatively low voltage. Moreover, the electrical properties after the phase transformation are particularly suitable for fabricating a memory. Furthermore, the area occupation of the chalcogenide random access memory (CRAM) is only ⅓ of the magnetic random access memory (MRAM) and the ferroelectric random access memory (FeRAM) and the CRAM can easily integrate with a logic circuit. Therefore, CRAM has gradually become one of the most promising techniques for producing a whole new generation of memory products, especially for miniaturized portable products.
The chalcogenide RAM store data by effecting a phase transformation through the power source controlled by a transistor. However, the current that can be provided by a transistor is quite limited. Hence, one major issue is to achieve a balance between the operating current of the chalcogenide RAM and the current range provided by the transistor.